One of the surface emission type semiconductor lasers has been reported in Extended Abstracts (The 50th Autumn Meeting, 1989); The Japan Society of Applied Physics, Volume 3, pp. 909, 29a-ZG-7, issued on Sep. 27, 1989. FIG. 45 shows a perspective view of a light emitting unit in such a semiconductor laser. The semiconductor laser is produced through the following process. An n-type GaAs substrate 2202 is first processed to grow n-type AlGaAs/AlAs multilayer film 2203, n-type AlGaAs clad layer 2204, p-type GaAs active layer 2205 and p-type AlGaAs clad layer 2206 thereon. The substrate 2202 is then etched to leave a column-like region 2220 which is buried by AlGaAs layers 2207, 2208, 2209 and 2210 formed sequentially in the order of p-type, n-type, p-type and p-type. Thereafter, a dielectric multilayer film 2211 is deposited on the top of the p-type AlGaAs cap layer 2210 and n-type and p-type ohmic electrodes 2201, 2212 are then formed. Thus, a surface emission type semiconductor laser will be formed.
In the surface emission type semiconductor laser of the prior art shown in FIG. 45 the embedding layers 2207 and 2208 provide a p-n junction as means for preventing an electric current from flowing to parts other than the active layer. However, with the p-n junction it is very difficult to provide a sufficient current constriction and a non-effective current cannot be completely suppressed. In the prior art, therefore, it is difficult to perform a continuous oscillation drive at room temperature due to the joule effect heat in the laser elements being increased by such non-effective current. In the laser of the prior art, the entire optical resonator is buried by a material having its refractive index lower than that of the resonator. Thus, light will be confined in the resonator. Even if the cross-sectional configuration of the resonator in a direction parallel to the plane of the resonator substrate is changed, the light emission spot in the basic oscillatory mode will be formed into a dot-like shape having its diameter equal to about 2 .mu.m. When it is desired to form a surface emission type semiconductor laser into a two-dimensional array configuration by which the laser is characterized, it is difficult to use a plurality of independent resonators to provide a single and stable laser beam from the laser beams of the respective resonators due to interference since the laser beams from the individual resonators are not equalized in phase even if the resonators are located close to one another in the substrate plane.
FIG. 46 shows a cross-sectional view of another surface emission type semiconductor laser according to the prior art. Such a laser is structured by forming n-type distributed Bragg reflection (DBR) type mirror 2402, n-type clad layer 2408, quantum well active layer 2403, p-type clad layer 2409, p-type DBR mirror 2404 and p-type ohmic electrode 2405 on n-type GaAs substrate 2401. The single crystalline state in a hatched region 2406 is then broken by implanting hydrogen ions thereinto to form a high-resistance region such that an injected current will only concentrate into the oscillatory region. An n-type ohmic electrode 2407 is formed on the underside of the substrate 2401. Light is emitted from the laser in a direction 2410 perpendicular to the plane of the substrate 2401.
In the surface emission type semiconductor laser of the prior art shown in FIG. 46, the injected current will flow through the p-type DBR mirror 2404. In the p-type DBR mirror 2404, the current flows in the form of positive holes as carriers. A positive hole has an effective mass about ten times larger than that of an electron and cannot well move beyond the heterobarrier within the mirror. Thus, the p-type DBR mirror 2404 presents an increased resistance component. The surface emission type semiconductor laser of the prior art shown in FIG. 46 must increase the number of mirror layers to increase the reflectivity in the p-type DBR mirror 2404. This raises a problem in that the resistance is very high in the p-type DBR mirror 2404.